1. Field of the Invention
The present invention relates to a plasma etching method.
2. Description of the Related Art
An etching method is known that switches a process from one etching process to another etching process while maintaining plasma (which is hereinafter referred to as an “etching method using continuous plasma), for example, when etching a multi-layered film.
In the etching method using the continuous plasma, conditions in a chamber switch as well as a gas when switching between two etching processes. This causes discharge conditions of the plasma to change, which is likely to generate high-frequency reflected waves. When many high-frequency reflected waves are generated, the plasma becomes unstable, which makes it difficult to perform an aimed plasma process. To prevent this, as disclosed Japanese Patent No. 5014435, a technology is proposed of suppressing the reflected waves of high frequency by tuning frequency of a high frequency power source when switching the gas. This can stabilize the plasma and can prevent the high-frequency reflected waves.
However, in the etching method using the continuous plasma, when different gases are used in two of the etching processes, a period of time when the different gases are mixed in a chamber is generated. When the etching progresses while the gases are mixed, an undesired etching may be performed in the switching process because the etching in the switching process is not performed by the gases in accordance with the process conditions according to a process recipe. Hence, in the switching process, making the etching uniform by suppressing the high-frequency reflected waves and preventing the progress of etching by supplying high frequency power with low energy are desired.